The present invention relates to a brake booster, in particular for automotive vehicles, having a vacuum casing divided into a vacuum chamber and a working chamber by a wall substantially of rigid and plate-shaped design and axially movably arranged in the vacuum casing, and a tube extending through the vacuum casing axially having its ends fastened to the end walls of the vacuum casing with the axially movable wall slideably sealed to the outer surface thereof. A mechanically actuatable control valve adapted to connect the working chamber to the vacuum chamber pressurized by vacuum, or to connect the working chamber to atmosphere has a control valve housing axially movably guided in the tube and rigidly connected to the axially movable wall through longitudinal slots in the tube. A push rod for a master brake cylinder is connected to the valve housing or to the axially movable wall.
A brake booster of the aforementioned type is described in the copending U.S. patent application Ser. No. 061,113, filed July 26, 1979 of J. Belart and F. Wieneike assigned to the same assignee as the present application.
In this known brake booster, the slots through which the axially movable wall is connected to the valve housing of the control valve are formed close to the working chamber in the tube extending through the vacuum casing. The axially movable wall is guided on the tube adjacent the end of the slots remote from the working chamber in a sealed relationship to the tube, the length of this guiding on the tube corresponding to the booster travel of the axially movable wall. The disadvantage of this arrangement is that it requires a large overall length, with the overall length being defined as the distance between the end walls of the vacuum casing because it is on these end walls that the mounting flanges are provided.
Further, the arrangement of the recesses on the end of the tube close to the working chamber makes it necessary for the valve housing in the tube to extend up to the end of the recesses remote from the working chamber in order to be guided in the tube in a sealed relationship thereto, otherwise a short circuit would exist between working chamber and vacuum chamber.
The connection of the axially movable wall with the valve housing is established by a split disc which is secured to the axially movable wall by screws and engages, with its radially inwardly extending area, grooves formed on the cylindrical outer surface of the valve housing.
Assembly of the split disc to provide a connection between the axially movable wall and the valve housing is possible with difficulty only, because the connecting members, such as disc and screws, are not easily accessible.